This invention relates to computer printers, and particularly to media transport mechanisms and methods of aligning media sheets for printing.
For accurate printing, it is important to align the print media with a print engine that will generate an image on the media. Any skew of the media will lead to an apparent skew of printing on the resulting printed sheet. Accordingly, printers have employed various techniques for xe2x80x9cde-skewingxe2x80x9d media after it is drawn from a stack or supply, and before printing.
One de-skewing technique is to advance the leading edge of a sheet against the nip of a pair of stationary and closed rollers, so that the groove defined by the rollers tends to trap the sheet edge. If one corner of the leading edge reaches the groove early, due to a skew, it is trapped in the groove as the other corner proceeds into the groove. Then, the sheet is advanced by rotating the rollers, and the sheet maintains the alignment provided by the process.
While effective for many applications, this approach still permits some degree of skew error. The elastomeric rollers required for effective transport of the sheet tend to catch the sheet edge, so that both corners do not necessarily fully lodge deep in the groove; one corner may stop slightly prematurely due to the friction involved. Other de-skewing techniques are considered to be disadvantageous due to the cost or bulk required for their mechanisms, or the delay introduced into a printing process where throughput rate can be important.
The present invention overcomes the limitations of the prior art by providing a printer having a media transport mechanism defining a media path. The path extends from a media supply past a print engine. A media alignment element moves between an extended position intersecting the path between the supply and the engine, and a retracted position away from the path. The printer may include a pair of rollers between the supply and the alignment element and encompassing the path, so that the sheet may be gripped by the rollers at a position adjacent the alignment to preserve the alignment by the element. The rollers may retract the sheet from the alignment element, which may move aside from the media path, so that the media may be fed toward a print engine.